a. Field of Invention
The invention relates generally to a remote entry chirp for a vehicle, and, more particularly, to a remote entry chirp sound reduction method and system that utilizes a conventional traffic horn and controls pulse duration as a function of one or more vehicle characteristics, such as system voltage, the time since turning the ignition OFF, and/or temperature.
b. Description of Related Art
Many vehicles are configured to provide a locking and/or unlocking confirmation tone (e.g., chirp) for the Remote Keyless Entry (RKE) system. The chirp may be generated using the vehicle's conventional traffic horn in an effort to reduce cost and stay competitive in the automotive field. The sound pressure level (dBA) output of the traffic horn must meet a minimum regulation for traffic use which is often too loud for RKE applications. The regulation intent for the traffic horn is designed to ensure that the vehicle provides sufficient sound to achieve the traffic horn's primary purpose of alerting other drivers or pedestrians when the driver actuates the horn switch and/or pad. The regulation requires a minimum of 93 dB measured at 7 meters in front of the vehicle (see FIG. 1). In order to meet this requirement, each horn or dual-horn assembly is usually placed close to the front of the vehicle (e.g., just behind the grille) to ensure optimal sound delivery for traffic situations. Chirps or confirmation tones utilizing the vehicle's conventional traffic horn placed in this front location generally emit too much sound for the locking/unlocking confirmation tones associated with the RKE applications. Chirps or confirmation tones utilizing the vehicle's conventional traffic horn may be considered too loud or may not convey a pleasant and/or luxurious sound to a typical consumer.
Some vehicles (e.g., luxury vehicles) may install a separate locking/unlocking chirp sounder for the RKE system and package it deep in the engine compartment to help reduce the sound level. However, the use of a separate locking/unlocking chirp sounder, along with the associated wiring and bracket, can increase the cost per vehicle.
For those vehicles that cannot incur the added cost of a separate locking/unlocking chirp sounder, attempts to reduce and/or minimize the locking/unlocking chirp sound level have focused on reducing a traffic horn pulse duration to prevent the traffic horn from reaching peak sound pressure level. However, as the pulse is reduced (e.g., below 40 ms), there may be a risk that the horn or dual-horn assembly may not start up due to a lack of adequate time to place the horn plates in oscillation. This risk may be greatest, for example, at low voltage and high temperature due to less energy and higher circuit resistance. Further, if the pulse is too short, the horn or dual-horn assembly may make poor quality and/or awkward sounds. Failure to start (e.g., begin oscillating) and/or poor quality horn sounds may result in increased horn and vehicle warranty claims due to the intermittent performance of the horn.
Accordingly, a decision may be made to rely on selecting the pulse duration that is sufficiently long to ensure start-up of the horn or dual-horn assembly in a worst-case scenario (e.g., even under the worst case conditions presented by (1) minimum battery voltage; (2) maximum operating temperature of the horn or dual-horn assembly; (3) maximum operating temperature of the wiring between the horn and the battery; and (4) the part-to-part distribution of the horn's or dual-horn assembly's electrical circuit). This may result in too long of a pulse at nominal voltage and room temperature, which may result in an unpleasant (e.g., too loud) chirp in many usage scenarios (e.g., (1) maximum battery/alternator voltage when chirps are performed with the engine running; (2) maximum battery voltage when chirps are performed with the engine OFF; (3) minimum horn temperature; and (4) minimum wiring temperature). The unpleasantness (e.g., loudness) of the chirp may be increased if commanded right after the vehicle is turned OFF since the system voltage can be as high as approximately 13.5 to 16 V if the vehicle was running. Typically, after a vehicle is turned OFF, the battery voltage may decay to approximately 12.4 V after a few minutes, assuming a good state of charge. If the pulse duration is not configured to ensure traffic horn performance in a worst-case scenario, then there will be some margin of intermittent operation under certain conditions, which may risk warranty and customer dissatisfaction.
Exemplary sound reduction methods in the prior art have focused on variation of the audible signal based on the transmission distance between a remote transmitter and a controller located in the vehicle (e.g., U.S. Pat. No. 6,049,268 issued to Flick) or on the ambient noise levels in or around the vehicle (e.g., U.S. Pat. No. 6,927,685 to Wathen), but have not addressed other parameters (e.g., specific vehicle conditions) that may significantly affect the volume of locking/unlocking confirmation tones or chirps for a RKE system.
Accordingly, there remains a need for a remote entry locking/unlocking confirmation tone and/or chirp for a vehicle that is less loud and/or unpleasant, with the tone/chirp still utilizing the existing traffic horn. There also remains a need for a method and system which allows for variation and/or adjustment of the pulse duration for the traffic horn depending upon measured and/or estimated conditions of the vehicle, including, for example and without limitation, vehicle system voltage and traffic horn temperature. Yet further, there remains a need for a method and system which allows for a pulse duration that is below the minimum pulse duration required in a worst-case scenario (e.g., low voltage and high temperature), while still ensuring actuation of the traffic horn for a RKE system.